Writing data to an optical disc

ABSTRACT

When writing data to an optic disc with a constant linear velocity, and encountering a disc error, data is written into the defect management area of the disc without changing the rotational speed of the disc, or at least without changing the rotational speed of the disc sufficiently to maintain a constant linear velocity. This allows an increase in the rate at which data may be written to the optical disc. It also avoids or reduces the need for the rotational speed of the disc to be changed, which allows a further improvement in the time taken to write data to the disc. In order to continue writing data to the disc without changing the rotational speed, the data rate must be increased while writing to the defect management area. For this to be possible, the data must be written into an “iced” or unformatted part of the defect management area.

TECHNICAL FIELD OF THE INVENTION

This invention relates to optical discs, and in particular to a methodand apparatus for writing data to an optical disc.

BACKGROUND OF THE INVENTION

Optical discs are commonly used for data storage. That is, data iswritten to and read from such discs, by means of an optical source.

In order to maximize the data storage capacity of an optical disc, datais written to the disc with a fixed data density. That is, the spatialseparation of the data points on the disc is constant. In order to allowa constant data rate, while data is being written to or read from thedisc, the disc is rotated with a constant linear velocity (CLV). Thatis, the angular velocity varies, as the optical source moves from onepart of the optical disc to another. Specifically, the disc rotates witha higher angular speed when data is being written to or read from aninner part of the disc, and with a lower angular speed when data isbeing written to or read from the outer part of the disc.

Different optical disc formats are known, and, in some formats, a discis provided with one or more defect management areas, which may forexample be located in the radially outer part of the disc. One suchformat is defined in the Mount Rainier specification, which is describedfor example in the document “Mt Rainier An Explanation” published byKoninklijke Philips Electronics NV, and available on the internet inNovember/December 2002 at www.mt-rainier.org. The defect management areamay be used when writing data to the disc. If an error occurs whilewriting data to the disc, for example because of a defect in the disc,the data is written to the defect management area of the disc instead.

However, as mentioned above, in order to maintain the same data rate(that is, the same number of bits of data which are written to the disceach second), while writing to the outer area of the disc, it isnecessary to decrease the rotational speed of the disc. Similarly, whenwriting to the defect management area has ended, it is again necessaryto change the rotational speed of the disc, when returning to writingdata into the main data region of the disc.

This has the disadvantage that it takes a noticeable time for therotational speed of the disc to be changed to the required value, withthe necessary degree of accuracy. As a result, writing data into thedefect management area significantly increases the time taken to writethe data. Similar problems arise when reading data which has beenwritten into the defect management area.

SUMMARY OF THE INVENTION

According to an aspect of the present invention, these problemsassociated with the prior art are at least partly alleviated by writingdata into the defect management area of the disc without changing therotational speed of the disc, or at least without changing therotational speed of the disc sufficiently to maintain a constant linearvelocity.

This allows an increase in the rate at which data may be written to theoptical disc. It also avoids or reduces the need for the rotationalspeed of the disc to be changed, which allows a further improvement inthe time taken to write data to the disc.

In order to continue writing data to the disc without changing therotational speed, it follows that the data rate must be increased whilewriting to the defect management area. For this to be possible, the datamust be written into an “iced” or unformatted part of the defectmanagement area.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block schematic diagram of an optical disc writing device,in accordance with an aspect of the present invention,

FIG. 2 shows relationships between the rotational speed of an opticaldisc and the radial position of the optical head of the disc writingdevice,

FIG. 3 shows an optical disc for use in connection with the invention,and

FIG. 4 is flow chart illustrating a method in accordance with an aspectof the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows a DVD+RW writer device 10, for writing data to an opticaldisc 20. The device 10 operates in the DVD+RW format, for example asdefined in the Mount Rainier standard. The disc 20 is mounted on aturntable (not shown), which is rotated under the control of a discdrive 22, which is in turn controlled by control circuitry 24. Thecontrol circuitry 24 also controls the operation of an optical head 26,which generates the optical signals which are used to write data ontothe disc 20. The optical head 26 uses data which are stored in a memory,for example a RAM 28, again under the control of the control circuitry24.

It should be noted that, although the control circuitry is shown as asingle block, this may be in the form of one or more circuit blocks,plus associated components.

The control circuitry 24 has an input bus 30 which, in the writingprocess, is used for receiving data from a host computer or otherdevice.

Thus, for a given rate at which data is to be written onto the disc 20,and for a given radial position of the optical head 26 relative to thedisc 20, the control circuitry 24 ensures that the disc drive 22 causesthe disc 20 to rotate at the intended rotational speed. The intendedrotational speed R is given by:R=D·s/C  (1)where:

D is the intended data rate in bits per second;

s is the spatial separation of the data bits on the disc; and

C is the circumference of the disc at that radial position.

FIG. 2 shows relationships between the radial position of the opticalhead 26 relative to the disc 20, and the intended rotational speed R.Specifically, the line A illustrates the relationship given in equation(1) above, for radial positions between P1 at the inner edge of the discand P2 at the outer edge of the disc.

As described so far, the system is conventional, and so it will not bedescribed in more detail, as the necessary information is well known tothe person skilled in the art. However, the detail of the operation ofthe device, under the control of the control circuitry 24 is differentfrom the control of known devices, as will be described further below.

FIG. 3 shows an optical disc 20 for use in accordance with theinvention. The disc 20 has an inner region 40, which includes a lead-inarea, a general data storage area 42, and an outer region 44 (not shownin more detail).

As described in the document “Mount Rainier An Explanation”, referencedabove, the outer region 44 of the disc 20 includes a defect managementarea, to which data may be written in the event of an error whilewriting to the main data storage area 42 of the disc 20.

To allow its use in the present invention, the defect management areaneeds to be at least partially iced. That is, at least a part of thedefect management area is unformatted. It is known, for example fromU.S. patent application U.S. 2001/0043539 A1, that a DVD+RW drive isable to write data to an unformatted region of a disc at a higher linearvelocity, and hence at a higher data rate, than when writing data to aregion in which data has already been recorded, including a formattedregion of the disc.

A new disc is completely iced, and so no action needs to be taken toensure that there is a suitable iced region in the defect managementarea.

However, if the disc has previously been used, it is possible that thedefect management area will not be completely iced. Indeed, according toone existing version of the Mount Rainier standard, a disc (includingthe defect management area) should be fully de-iced, or a temporarylead-out should be written before any iced area.

If the defect management area is partly de-iced, for example becausedata has previously been written to a section of the defect managementarea, then it is possible to locate a region of the defect managementarea which remains iced.

If the defect management area is entirely de-iced, for example becausedata has previously been written to the whole defect management area, orbecause the disc has been formatted, then it is possible to “re-ice” thedefect management area or a region of the defect management area,preferably during a background process before beginning to write data tothe disc.

FIG. 3 is a flow chart showing a method of writing data to the disc 20,in accordance with the present invention.

The illustrated process begins with step 46, which takes place as partof a background process, before the writing of data begins. In step 46,it is determined whether the defect management area of the disc includesan iced area. If so, no further action is required, and it is determinedthat the disc is ready for data to be written to it.

However, if it is determined in step 46 that there is no iced region inthe defect management area of the disc, the process passes to step 48.In step 48, again as part of the background process before beginning towrite data to the disc, one or more regions in the defect managementarea of the disc is re-iced. The location of the iced area or areas isstored in a Formatting Disc Control Block (FDCB) on the disc.

In step 50, a block of data is written to the main data storage area onthe disc 20. In step 52, it is determined whether an error has occurredin writing this data. Assuming that there is no error, the procedurepasses to step 54, in which it is determined whether there is anyfurther data remaining to be written. If no further data remains, theprocess passes to step 56 (described below) but, if there is more dataremaining to be written, the process returns to step 50 and the writingof the data resumes.

If it is determined in step 52 that there was an error writing the blockof data to the intended section of the main data storage area, theprocess passes to step 58. In step 58, an iced area in the defectmanagement area 42 is identified, and the procedure then passes to step60. As mentioned above, the defect management area may be entirely iced,or partly iced. In either case, it is necessary to locate an iced areawhich is free for data storage. For example, as mentioned above, thisinformation may be stored in the Formatting Disc Control Block (FDCB) onthe disc.

In accordance with the invention, the disc drive 22 is caused to rotateat the same rotational speed, when writing to the iced area in thedefect management area 42, as would have been used when writing to theintended location in the main data storage area of the disc.

This is illustrated in FIG. 2. Thus, in the case of an error occurringwhile writing to the disc at the radial position P3 and at acorresponding rotational speed R3, data may be written to an iced areain the defect management area at a radial position P4. However, insteadof reducing the rotational speed of the disc to R4, as line A wouldindicate, the rotational speed of the disc is maintained at R3.

Based on equation (1) above, therefore, it can be seen that, since thecircumference of the disc will be larger at that radius, and since it isnecessary to maintain the spatial separation of the data bits at thesame value, the data rate must be increased.

In step 60, therefore, the control circuitry 24 determines the data ratewhich is necessary to allow the rotational speed to be maintained at theprevious value, and, in step 62 of the process, the control circuitry 24controls the RAM 28 to output data to the optical head 26 at thenecessary increased data rate, and controls the optical head 26 to writethe data into the disc management area at the increased data rate.

In an alternative embodiment of the invention, the disc drive 22 may notbe caused to rotate at exactly the same rotational speed, when writingto the iced area in the disc management area 42, as would have been usedwhen writing to the intended location in the main data storage area ofthe disc. Instead, when writing to the iced area in the disc managementarea 42, the disc drive 22 may be caused to rotate at some speed whichis less than the speed which would have been used when writing to theintended location in the main data storage area of the disc, but whichstill requires that data be written at a higher data rate than normal,based on equation (1) above. Using FIG. 2 to illustrate this again, inthe case of an error occurring while writing to the disc at the radialposition P3 and at a corresponding rotational speed R3, and with thedata being written instead to an iced area in the defect management areaat the radial position P4, the rotational speed of the disc may bereduced to some speed R5, where R3>R5>R4.

When data has been written to the iced area in step 62, the processpasses to step 54, in which it is determined whether there is more dataremaining, as described above.

When the writing is completed, the process passes to step 56. At thisstage, in order to ensure that the disc complies with the Mount Rainierstandard, any necessary re-formatting is performed. For example, if thedisc is not yet completely written and de-iced, the defect managementarea at the outer side of the disc is copied after the last user data,so that the lead-out occurs immediately after this copy of the defectmanagement area, ensuring DVD-ROM compatibility. Alternatively, if theuser data area of the disc is completely written, any remaining icedareas in the defect management area are de-iced. The process then passesto step 57, and ends.

It will be noted that this description, and the flow chart of FIG. 4,assume that there is sufficient time for the re-icing of a region in thedefect management area to be completed (in step 48), before starting towrite data to the disc (in step 50). However, in some situations it isrequired to begin writing data to the disc immediately on insertion. Inthat case, it is not possible to re-ice the disc, or to completere-icing of the disc, before beginning writing data to the disc. If anerror then occurs, data is written to the defect management area in theconventional way, that is, at a constant data rate, and therefore at areduced rotational speed of the disc.

In that case, the necessary background process, to re-ice a region ofthe defect management area, can be carried out when the user stopswriting data to, or reading data from, the disc.

Once data has been written to the disc, it must then be read from thedisc. In some situations, it will also be possible to maintain therotational speed of the disc constant, even when reading data from thedefect management area. Of course, in order to be able to do this, itwill be necessary for the disc reader to be able to read data at ahigher data rate than normal.

There is therefore disclosed an optical disc writing apparatus, and amethod for use in such an apparatus, which allows more efficient writingof data onto the disc, in particular when writing data to a defectmanagement area.

It should be noted that the term “comprises” or “comprising”, as usedherein, means that the stated features or elements are present, but doesnot exclude the possibility that additional features or elements mayalso be present. Similarly, the word “a” or “an” does not exclude thepossibility that a plurality of the stated features may be present.

1. A method of writing data to an optical disc, the method comprising: controlling a disc drive such that the optical disc is rotated at a first rotational speed which corresponds to a constant linear velocity, and writing data to the optical disc at a first data rate; and in the event of an error writing data to the optical disc; writing data into an unformatted region of a defect management area of the optical disc at a second data rate which is higher than the first data rate.
 2. A method as claimed in claim 1, comprising, in the event of an error writing data to the optical disc, controlling the disc drive such that the optical disc continues to rotate at the first rotational speed.
 3. A method as claimed in claim 1, comprising, in the event of an error writing data to the optical disc, controlling the disc drive such that the optical disc is rotated at a second rotational speed which is less than the first rotational speed.
 4. A method as claimed in claim 1, the method comprising, before writing data to the optical disc, ensuring that the defect management area of the disc comprises at least one unformatted region.
 5. A method as claimed in claim 4, wherein the method comprises, before writing data to the optical disc, determining whether the defect management area of the disc has at least one unformatted region and, if not, deformatting at least one region thereof.
 6. A method as claimed in claim 5, comprising performing the deformatting as a background process.
 7. A method as claimed in claim 1, further comprising, after writing data to the optical disc, formatting any remaining unformatted region of the defect management area of the optical disc.
 8. An optical disc writer, comprising a disc drive for rotating the optical disc, wherein the disc writer is adapted to write data to the optical disc at a first data rate while the optical disc is rotated at a first rotational speed which corresponds to a constant linear velocity, and wherein the disc writer is further adapted, in the event of an error writing data to the optical disc to write data into an unformatted region of a defect management area of the optical disc at a second data rate which is higher than the first data rate.
 9. An optical disc writer as claimed in claim 8, wherein the disc writer is adapted, in the event of an error writing data to the optical disc, to control the disc drive such that the optical disc continues to rotate at the first rotational speed.
 10. An optical disc writer as claimed in claim 8, wherein the disc writer is adapted, in the event of an error writing data to the optical disc, to control the disc drive such that the optical disc is rotated at a second rotational speed which is less than the first rotational speed.
 11. An optical disc writer as claimed in claim 8, wherein the disc writer is adapted, before writing data to the optical disc, to ensure that the defect management area of the disc comprises at least one unformatted region.
 12. An optical disc writer as claimed in claim 11, wherein the disc writer is adapted, before writing data to the optical disc, to determine whether the defect management area of the disc has at least one unformatted region and, if not, to deformat at least one region thereof.
 13. An optical disc writer as claimed in claim 12, wherein the disc writer is adapted to perform the deformatting as a background process.
 14. An optical disc writer as claimed in claim 8, wherein the disc writer is adapted, after writing data to the optical disc, to format any remaining unformatted region of the defect management area of the optical disc.
 15. An optical disc writer as claimed in claim 8, wherein the disc writer is a DVD+RW disc writer. 